Hydrophobic organic liquids, such as mineral oil or the like, are frequently used as impregnating agents, because of their water-repellant and electrically insulating properties, for example for paper-insulated electrical cable, and/or as a filler material, for example in cable connections, electrical transformers and the like. In this connection, it is particularly advantageous that the liquid state of aggregation makes it possible to completely fill a given space without leaving cavities which can be deleterious, particularly in electrical installations. Furthermore, it is an advantage that many hydrophobic organic liquids have the property to creep even into smallest interstices. On the other hand, the use of a liquid as an impregnating or filling material requires a complete tightness of the enclosure into which the liquid is filled. This requirement often creates difficulties in practice. To circumvent these difficulties, it is known in the art to employ liquids which are solid at normal temperature and accordingly must be employed at elevated temperatures. In practical application, it is inconvenient to work at elevated temperatures and to provide therefore corresponding heating devices. Upon cooling-down, the liquid transforms into a solid mass which is no longer or still only slightly deformable; this is undesirable in several cases. Therefore, the use of industrial gelling agents has been reported which are added to the liquid and after a certain time form with the latter a gel which no longer can flow out through leaks and remains deformable. Known gelling agents of this kind contain organic aluminum compounds, particularly poly-oxo-aluminum compounds, which react with hydroxyl or carboxyl groups to form a thixotropic gel. In this manner, for instance, paints are provided with a, typically, desirable thixotropic property. Poly-oxo-aluminum compounds of the kind indicated are distributed, for instance, by the British company Manchem Ltd.
Frequently, hydrophobic organic liquids, particularly mineral oil or the like, do not comprise hydroxyl or carboxyl groups so that the gelling agents cannot react directly with these liquids. This is particularly true in electrical applications because impregnating and filling materials used therein do not contain, as a rule, hydroxyl or carboxyl groups. In such cases, therefore, a reactant, mostly in the form of a liquid, which contains the groups necessary for the gelling reaction were added upon the addition of the organic aluminum compound. For example, solvents which contain hydroxyl or carboxyl groups are suitable as a reactant. In a practical application, it is inconvenient to additionally add the reactant. Also, quantity errors may easily occur. Added thereto is the difficulty that the organic aluminum compounds react very strongly with moisture and thus must be stored and shipped under an air-tight seal and must be handled with great care.
In the course of the gelling reaction, the reactive groups of the reactant are converted into electrically unobjectionable compounds, whereby the insulating properites of the liquid improve gradually to an original value. This can be observed from the increase of the dielectric loss factor which can be easily measured. Normally, it will last several days until the electrical insulating properties of the gelled liquid have improved to the point where an operational electrical load is again possible. This long waiting time until the respective devices are put into operation is very inconvenient and causes considerable cost and time.
It is thus the object of the invention to provide an industrial gelling agent, particularly for electrical applications, which is more conveniently applicable and makes possible a reduction in the aforedescribed waiting times.